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import os
import subprocess
from .utils import get_video_dims
def render_segmented_overlays(ass_path, segments, video_path, output_dir):
"""
Renders segments using a physical transparent PNG canvas to ensure alpha correctness.
"""
width, height, _, fps = get_video_dims(video_path)
ass_path_sanitized = ass_path.replace("\\", "/").replace(":", "\\:")
# Generate Base Canvas
canvas_png = os.path.join(output_dir, "base_canvas.png")
subprocess.run([
"ffmpeg", "-y", "-f", "lavfi", "-i", f"color=c=black@0.0:s={width}x{height}",
"-frames:v", "1", "-c:v", "png", canvas_png
], stdout=subprocess.DEVNULL, stderr=subprocess.PIPE)
overlay_data = []
print(f"Rendering {len(segments)} subtitle segments (Mode: Canvas + QTRLE)...")
for i, seg in enumerate(segments):
start = seg.get('start', 0)
end = seg.get('end', 0)
duration = end - start
if duration <= 0: continue
filename = f"caption_{i}.mov"
out_path = os.path.join(output_dir, filename)
# QTRLE (QuickTime Animation) - The absolute reference for Alpha.
# Slightly larger files than PNG, but 100% compatible.
cmd = [
"ffmpeg", "-y",
"-loop", "1", "-i", canvas_png,
"-vf", f"format=rgba,setpts=PTS+{start}/TB,ass='{ass_path_sanitized}',setpts=PTS-{start}/TB,format=rgba",
"-t", str(duration),
"-c:v", "qtrle",
"-pix_fmt", "argb", # qtrle uses argb pixel format usually
"-an",
out_path
]
try:
subprocess.run(cmd, check=True, stdout=subprocess.DEVNULL, stderr=subprocess.PIPE)
rel_path = os.path.join("captions", filename).replace("\\", "/")
overlay_data.append({ "path": rel_path, "start": start, "end": end, "index": i })
print(f" [Seg {i}] Rendered {duration:.2f}s")
except subprocess.CalledProcessError as e:
print(f" [Seg {i}] Failed: {e}")
if os.path.exists(canvas_png): os.remove(canvas_png)
return overlay_data